Water analysis for sanitary purposes : with hints for the interpretation of results / by E. Frankland.

  • Edward Frankland
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: Water analysis for sanitary purposes : with hints for the interpretation of results / by E. Frankland. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    as o^reat as the total bulk of the concentrated filtrate must, in all, be introduced into the tube. 13j careful manipulation, it is easy to introduce successively the concentrated liquid and the rinsings into the tube by means of the cup and stopcock without the admission of a trace of air. If, however, air .should inadvertently gain admission, it may, if of considerable volume, be withdrawn by suction applied to the cup (/y), the stopcock being momentarily opened. A minute bubble of air may be expelled by pressing the thumb firmly against the opening at the bottom of the tube and momentarily opening the stopcock. If a trace of gas is liberated immediately on the addition of sulphuric acid, it will consist of carbonic acid, and must be expelled. The evolution of nitric oxide does not take ])Iace until a minute or two after the violent agitation of the contents of the tube. The tube is now undamped, and so grasped that the moist thumb can firmly close the opening at the bottom, and being withdrawn from the trough, it is then violently agitated. The tube, dui’ing this operation, is inclined at a considerable angle, the cup pointing away from the operator. Holding the tube in this way, and briskly shaking it in a vertical direction, it is easy to impart a combined vertical and lateral movement to the liquids, which soon reduces the mercury near the acid to a state of fine division, without, however, breaking the continuity of that in the lower part of the tube. If nitrates or nitrites are present, a considerable pressure is soon felt against the thumb, and mercury spurts out in minute streams, as nitric oxide is evolved. The escape of the gas should be resisted, so as to maintain a considerable excess of pressure inside the tube, and thus prevent the ])0ssibility of air gaining access to the interior during the shaking. The shaking must be continued till no more gas is given ofl^. The time required for this varies from three to five or six minutes. When the quantity of nitrates is considerable, the nitric
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